It is sometimes necessary at a construction site or along a proposed path of underground utility lines to lower the water table level. One of the methods presently used for the removal of water to lower the water table is the use of vertical wellpoints. Wellpoints are most commonly used in areas which already have some buried obstruction, such as a utility line, making digging of a trench unsuitable. By this wellpoint procedure, a perforated pipe is inserted into a vertical hole to a suitable depth into the ground. The top end of the pipe is connected to a suction pump or to a horizontal pipe located on the ground which interconnects the tops of a series of vertical wellpoints. The horizontal pipe is connected to a suction or vacuum pump. The pump draws water up from the vertical wellpoints that has entered the perforated pipes. The depth of the vertical pipe depends on the suction capacity of the suction pump to raise water from a predetermined depth.
In an alternate wellpointing method, horizontal wellpoint pipe is placed at the bottom of a trench and subsequently covered by soil excavated during digging of the trench. A suction pump is attached to an above-ground end of the pipe to draw up water that enters the pipe until the water table is lowered.
An example of a method of laying drainage pipe is disclosed in U.S. Pat. No. 3,874,182 to Potter et al. In this patent, horizontal wellpoint drainage pipe is buried by excavating a trench using a mechanical digging apparatus. The excavated soil is directed away from the trench. The wellpoint drainage pipe located at the bottom of the trench is covered by backfilling the trench wholly or partially with water-pervious material, other than the excavated soil, so as to promote the flow of ground water to the pipe.
Another method of laying horizontal wellpointing pipe is disclosed in U.S. Pat. No. 3,998,065 to Darnell. In the Darnell patent, a trenching vehicle digs a trench while perforated flexible pipe having a filter material is placed along the bottom of the trench. The pipe is covered as the trench is refilled, and a subsequent evacuating pressure is applied to the pipe by an above-ground pump. As shown in FIG. 5 of the Darnell patent, the trenching mechanism, for initiation of the trench, contacts the ground at an angle of approximately 45.degree.. Then, as described in the patent, the trenching mechanism is activated and rotated to a slightly vertical position for burying non-perforated pipe for later connection to a suction pump. Similarly, withdrawal of the trenching mechanism appears to be along the same line as the initial digging of the trench, whereby the trenching mechanism is moved from its slightly inclined to the vertical position to an angle of approximately 45.degree. along an arc so that the trenching mechanism, when removed from the earth, is at an angle of approximately 45.degree..
In U.S. Pat. No. 4,397,585 to Fouss et al., an apparatus for inserting foldable conduit below ground is disclosed. A plow lifts the soil to a sufficient height to form a cavity or trench immediately behind the plow. The soil loosened by the plow falls by gravity around a circular conduit laid down behind the advancing plow blade.
U.S. Pat. No. 3,583,168 to Horton discloses a backfill and pipe laying attachment for a side discharge trencher. By this invention, a trench being dug for the reception of pipe is backfilled behind the trencher. An attached vehicle moves along behind the trencher and backfills the trench dug by the trencher, while at the same time pipe is laid along the bottom of the trench.
U.S. Pat. No. 3,332,249 to Idoine discloses a trench digging and refilling apparatus, in which a circular, horizontally oriented conveyor discharges dirt excavated by a digging unit for discharge rearwardly into the trench or laterally alongside the trench, depending on the direction of movement of the circular horizontal conveyor.
Additional examples of earth-excavating equipment are disclosed in U.S. Pat. Nos. 327,274 to Keith, 1,814,094 to Rhodes, 333,114 to Dougine, 946,609 to Loomis, and 3,831,388 to Wells. A rock excavating machine is disclosed in U.S. Pat. No. 2,935,801 to Stewart II et al.
Each of the cited patents requires a large area over which a digging operation is initiated, with a majority of the references including trenching machines which start at a distance from the drive vehicle and are moved towards the drive vehicle until being located in a digging position. A large amount of clearance is thereby required to begin the digging operation so as to have the lowermost point of the trenching machine reach a lowermost point of the trench to be dug.